This web site is dedicated to providing free software specific to transmission lines and their characteristic behavior. All software at this web site was written by Robert Lay, licensed as W9DMK in March 1948. In addition to the free software you will find interesting articles, such as "Transmission Lines for Dummies", "The Quarter Wave Transformer", and "Observations on the Maximum Power Transfer Theorem".

Some of the software listed below is written in Visual Basic for DOS and will run on any DOS or Windows machine except NT based systems (i.e., Windows NT, Windows 2000, or Windows XP). Some programs are written in "C" for DOS and will run on any DOS or Windows machine. Some programs are written in Visual Basic for Windows or in Visual C++ for Windows and will run on all 32 bit Windows systems.

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Click on any program name to download its zip file!


 COAX_Z - A DOS program written in "C" that takes you through the measurement of the characteristic impedance (Zo) of a piece of coax. Based on the equations in the ARRL Antenna Book, this program produces the Ro, Xo, Velocity Factor and other useful data about the line. Runs on any DOS or Windows system.

 LSECT - A program that designs "L" matching sections to transform an antenna impedance to a specified value, such as 50 ohms. Written in Visual Basic for DOS. Requires the VB for DOS runtime module - see below.

LSECTW – The Windows version of LSECT program above. Design “L” matching sections. Written in VB 6.0, the zip file is about 1.8 MB and includes an extensive Help file and the full Windows installation package for all versions of Windows..

 NCS - A net control program - very useful for maintaining a simple data base for use in calling the roll and keeping track of attendance and traffic. Includes a Help file and incorporates a Windows installation program. Can be easily configured to display your own net's name and logo.

 NEWWAV - Similar in functionality to SWAVE but in a more compact program for DOS. Accepts non-zero reactance component in the line impedance and allows negative line lengths. It also writes the results to a disk file for future reference or printing out.

   QT - A text insertion program that allows you to save often-used text phrases and insert them into your typing stream with hot-keys. Includes Help file and incorporates a Windows installation program.

 RFBR- A program that computes impedances from measurements made with a General Radio Model 1606 or similar RF Bridge. Dial readings and frequency are input and the impedance is calculated. The special feature of this program is that it performs the necessary calculations to convert from a three-measurement sequence to compute the impedance of a balanced load being measured by an unbalanced bridge. Requires the VB for DOS runtime module - see below.

RFBRWIN - Same as RFBR, above, except written in Visual C++ for Windows. Works in NT-based systems, such as Windows NT, Windows 2000 and Windows XP.

 SMCHR - The Smith Chart program with its extensive Help files. Written in Visual C++ ver 1.5, it runs in Windows 3.1 and later.

SMARTSMITH – Version 1.6.2 (12/06/04) written in Visual Basic 6.0 – this program is a smarter version of the Smith Chart program. It allows you to dynamically generate impedance point plots as you configure each design element of an impedance matching network. Much easier to use than SMCHR and also has an extensive Help file with a Wizard that tells you what steps to take in designing a matching network for a given load impedance. Complete Windows installation kit – about 2 MB zip file. Version 1.6.2 adds several features including better logging.

NETWORKPROCESSOR – The plotting package for SmartSmith - about 66 Kb.  Unzip this file into your SmartSmith application folder, and it adds the capability to display plots of voltage, current and impedance versus frequency for your SmartSmith matching network. Includes extensive help files.

 SWAVE - A Windows program for transmission lines - written in Visual Basic 3.0 for Windows. Includes the reactive component of characteristic impedance and allows negative values of line length. Requires the VBRUN300.DLL run time module - see below.

 SWR - Computes the Standing Wave Ratio, given the power readings on a line.

 TLE - Transmission Line equations for Windows. Written in Visual C++. This program provides the most comprehensive analysis of a transmission line available from this site. In this release, the possibility of non-zero reactance for Zo is introduced. If you are interested in the best of the programs available on this topic from this site - this is it.

 VECTORS - A program that does complex arithmetic. If you are challenged by vector arithmetic and want to avoid the cumbersome procedure for adding, subtracting, multiplying or dividing vectors or complex numbers, then you will like this program. Requires the VB for DOS runtime module - see below.

VECTORSW – The Windows version of the Vectors program, above. It’s a complex arithmetic calculator. Solve difficult circuits in minutes with Vectors or Phasors. Written in VB 6.0, the zip file is about 1.8 MB and includes an extensive Help file and the full Windows installation package for all versions of Windows..

 XMSL - Transmission Line program that computes the points of maximum current in the standing wave pattern. Written in Visual C++.

XLINE - This Windows program is another implementation of the Transmission Line Equations for the Windows environment, similar to TLE or SWAVE programs, above. Written in Visual Basic 6.0, this program is unique in that it features a spin control for purposes of rapidly changing the length of line. In addition to the VB runtime module, vbrun300.dll, this program also requires the additional module, mscomct2.ocx, which can be downloaded as a zip file, here.

Run Time Module for VB for DOS - .Visual Basic for DOS programs require the run-time module VBDRT10E.EXE. Zipped copy of this file is available by clicking on the link. After downloading and unzipping the file, save it in C:\ Windows\System or C:\Windows\System32..

The Maximum Power Transfer Theorem (MPTT) - Historically, the MPTT has been misunderstood - first from the standpoint of understanding all of its implications, and second from the standpoint of its effect on the maximum possible efficiency of a system. Consider the possibility of every system having to have its internal impedance equal to its load impedance. Would such systems be limited to 50% efficiency? What are the implications of the theorem as it applies to maximum power transfer? Does it mean that the system must be power limited? What are the implications of having the load impedance vary? Does that mean we cannot analyze the system by varying its internal impedance instead? These issues have been analyzed in an article that I hope will shed some light on practical issues such as "conjugate matching" and the efficiency of RF power amplifiers.  This is a rather large download in PDF format. You may want to use the right click pop up menu and select "Save target as…"

Goldman Steady-State Equations and Goldman Transient Equations - In 1949, Stanford Goldman, Professor of Electrical Engineering at Syracuse University, wrote his book, “Transformation Calculus and Electrical Transients”, which was published by Prentice-Hall, Incorporated as part of their Electrical Engineering Series, edited by W. L. Everitt. I have written two articles, one addressing the problem in the transient phase and the other addressing the problem in the steady-state. I found that Goldman’s work on transmission lines is the only published work that covers both aspects of the problem and provides a unified mathematical basis for each. The objective of these two articles is to try to bring the mathematical concepts outlined by Goldman to bear on specific, well known examples of the quarter wave matching transformer. The reader will find that no matter whether the transient or the steady-state model is pursued, the Goldman equations will provide a clearer picture of what really goes on in the transmission line. Each article begins with an explanation of the mathematical basis, which is then followed by a numerical example for a specific quarter wave matching transformer.



Transmission Lines for Dummies | The Quarter Wave Transformer | Maximum Power Transfer Theorem